A more thorough explanation:

Definition: Compulsory unitization is the process of collecting producing wells over a reservoir for joint operations, such as enhanced-recovery techniques, which is done by order of a regulatory agency. It is usually carried out after primary production has begun to fall off substantially, to permit efficient secondary-recovery operations. Compulsory unitization is also done to comply with well-spacing requirements established by state law or regulation.

Examples: An example of compulsory unitization is when a regulatory agency orders the collection of producing wells over a reservoir for joint operations. This is done to increase the efficiency of secondary-recovery operations and comply with state regulations.

Another example is when primary production has begun to fall off substantially, and the owners of mineral interests agree to unitize their wells to permit efficient secondary-recovery operations. This is called voluntary unitization.

Explanation: Compulsory unitization is a process that is carried out by regulatory agencies to increase the efficiency of secondary-recovery operations and comply with state regulations. It is usually done when primary production has begun to fall off substantially, and the owners of mineral interests agree to unitize their wells to permit efficient secondary-recovery operations. Compulsory unitization is different from voluntary unitization, which is arranged by agreement of the owners of mineral interests.